This invention relates to producing solid state devices by a plasma processing technique for feature delineation. More particularly, the invention relates to plasma etching of an irradiated resist film having at least one type of monomer locked into a host polymer to produce the desired negative resist pattern.
The making of photoresist or X-ray resist patterns used in the production of integrated circuits and other electronic devices normally requires the use of liquid chemical developing solutions. These solutions dissolve away either a previously irradiated portion of the resist, or the unirradiated portion, producing either a positive or negative tone resist pattern. The irradiated regions normally define the circuit geometry of the device, and so the ability of the liquid developer-resist combination to accurately reproduce the geometry desired is important.
One of the main factors limiting the ability of liquid developing techniques in achieving linewidths of approximately 1 .mu.m and less is the absorption of the developing solution by the resist during development. Such absorption causes the resist to swell in many cases, which distorts the linewidths and degrades the resolution obtainable. In addition, such absorption produces stresses in the resist film, which may cause the film to lose adhesion to the substrate.
While such absorption effects can be minimized by a judicious choice of developer and rinsing solvents, resolution is still limited to about 2 .mu.m gaps in 5000-7000 Angstroms final resist thickness for most current negative resists. Positive resists generally provide better resolution, but normally with reduced radiation sensitivity and inferior adhesion.
One way to avoid liquid developers is to use a plasma etch, such as oxygen excited by a radio frequency source. Plasmas have been used for several years to etch substrate materials, or for stripping away photoresists after a conventional liquid etch. They have also been used for selective etching when the pattern to be etched has first been defined by conventional means; see U.S. Pat. Nos. 3,816,196; 3,816,198. However, the use of plasmas to etch the pattern in the first instance is known by the present inventor is only one previous publication, German Pat. No. (Offen) 27 26 813.